1. Field of the Invention
The present invention relates to a key switch assembly for a computer keyboard, more particularly to a key switch assembly which has a relatively simple and stable structure with a reduced thickness.
2. Description of the Related Art
In co-pending U.S. patent application Ser. No. 09/031,414, now U.S. Pat. No. 5,878,872, issued Mar. 9, 1999 the Applicant disclosed a key switch assembly which includes a base board, a membrane circuit layer, a resilient layer, a scissors-type key cap support, and a key cap. The base board is formed with upwardly projecting slide retainer plates, upwardly projecting pivot retainer plates, and a stop projection. The membrane circuit layer and the resilient layer are superimposed in sequence on the base board, and are formed with aligned openings to permit extension of the slide retainer plates, the pivot retainer plates and the stop projection therethrough. The resilient layer is provided with an upright resilient member which is integrally formed with the resilient layer. The key cap support has a lower portion which is retained pivotally by the pivot retainer plates of the base board, and which is retained slidably by the slide retainer plates of the base board, and an upper portion which is retained pivotally by a pivot retainer unit of the key cap and which is retained slidably by a slide retainer unit of the key cap. The key cap is biased upwardly by the resilient member.
In order to impart an enhanced restoring force to the key cap, the resilient layer and the resilient member that is integrally formed therewith are typically formed from latex rubber, and the resilient layer typically has a thickness of about 0.3 to 0.5 mm. The restoring force of the key cap might be insufficient when the thickness of the resilient layer is decreased in order to reduce the thickness of the entire key switch assembly. As such, it is difficult to further reduce the thickness of the entire key switch assembly.
Moreover, the resilient layer formed from latex rubber is susceptible to deformation during transport thereof due to the surrounding temperature. This might affect the stability of the entire key switch assembly.